Catalytic hydrogenation of unsaturated hydrocarbons



7 June 1968 k R. a. cam; ETAL CATALYTIC HYDROGENATION OF UNSATURATEDHYDROCARBONS Filed April 15, 1966 ATTGEZVEZ United States Patent3,388,055 CATALYTIC HYDROGENATKQN 0F 'UNSATURATED HYDROCARBONS Robert G.Craig, Fairfax, Wilmington, DeL, and Lee Friedman, Bala Cynwyd, Pa,assignors to Air Products and tlhemicals, lino, Philadelphia, Pa, acorporation of Delaware Filed Apr. 15, 1966, Ser. No. 542,847 Claims.(Cl. 208-143) ABSTRACT 01* THE DISCLOSURE An unsaturated hydrocarbondistillate is fractionally distilled into three fractions. The middlefraction is catalytically hydrogenated in two reactors. The effiuentfrom the second reactor is mixed with the light fraction and eavyfraction. The mixture is then catalytically hydrogenated in a thirdreactor and a wash oil is added to at least one reactor.

The present invention relates to the catalytic hydrogenation ofunsaturated hydrocarbons having a high tendency to polymerize and moreparticularly, to the simultaneous partial and total hydrogenation ofseparate unsaturated hydrocarbon fractions for motor gasoline andaromatics production.

Unsaturated hydrocarbons boiling between about 75 to about 750 F. atatmospheric pressure, resulting from diverse conversion processes,including the catalytic and/ or thermal cracking of petroleum, thedestructive distillation of wood or coal, shale-oil retorting, etc.,frequently contain sulfurous, nitrogenous and oxygenated compounds whichrender them unsuitable for most applications without further processing.In addition to the aforementioned contaminants, such hydrocarbons alsocontain appreciable quantities of styrene and other mono-olefins anddi-olefins, the latter including compounds such as isoprene. An exampleof such unsaturated hydrocarbons is pyrolysis hydrocarbons, i.e.,normally liquid hydrocarbons boiling in the range of 77 to 500 F.,obtained as a by-product in the production of ethylene during the hightemperature pyrolysis of gaseous and/or liquid hydrocarbons.

Suggestions directed to the selective hydrogenation of mono-olefins and/or di-olefins, without simultaneously hydrogenating aromatic compoundspresent in these unsaturated hydrocarbons, have generally beenunsatisfactory due to such problems as comparatively low conversionrates, excessive colte make and catalyst deactivation. Especiallytroublesome is the presence of the di-olefins, which tend to formgum-like polymerization and co-polymerization products when heated toelevated temperatures of the order of 500 to 700 F. at which sulfur andnitrogenbearing compounds are effectively hydrogenated to products whichcan be readily removed by known techniques.

In conventional operations directed to the hydrogenation of unsaturatedhydrocarbons for motor gasoline production and aromatics production, itis necessary to cool, condense, fractionate and reheat between stageswith only the aromatics extraction feed portion being processed in thefinal stage. This interstage processing is expensive because itsubstantially duplicates similar processing at the outlet of the finalreaction stages.

In accor-.ance with the present discovery, these diniculties areefficiently and economically overcome by the simultaneous partialhydrogenation and total hydrogenation of selected and distinct fractionsof the unsaturated hydrocarbon charge. More specifically, in the presentinvention the raw unsaturated distillate to be processed is fractionatedto give cuts of the boiling range desired in 3,388,055 Patented June 11,1968 the finished product. The fraction to be produced completely freeof mono-olefins and diolefins is then processed in a two reaction zonesystem in the normal manner. The fractions to be only partiallyhydrogenated are introduced into the system at the outlet of the secondreaction zone and the combined fractions are then processed in a thirdreaction zone at the relatively mild conditions required for partialhydrogenation-the totally hydrogenated fraction from the second reactorserving to dampen the temperature rise efiect in the third reactor.Products of the desired boiling ranges are then separated byfractionation.

The process of the present invention may be understood more clearly byreference to the accompanying drawing which is a schematic illustrationof one particular embodirnent. In the interest of simplicity andclarity, various heaters, condensers, compressors, valves, controls,instruments, etc., have been eliminated from the drawing. In explanationof the drawing, the hydrocarbon charge stock will be assumed to be afull boiling range hydrocarbon distillate having an initial boilingpoint of about F., and an end boiling point of about 500 F. containingabout 1000 ppm. each of combined sulfur and nitrogen.

Referring to the drawing, the hydrocarbon charge stock is initiallyintroduced into the process fiow through line 1, being separated infractionator 2 to provide a light unsaturated gasoline fraction havingan end boiling point of about 160 F. leaving via line 3; an unsaturatedaromatics extraction feed fraction having a boiling point range ofbetween about 160 to about 295 F., leaving via line 4; and a heavyunsaturated gasoline fraction having an initial boiling point of about295 F., leaving via line 5. The fraction in line 4 is then passedthrough heat exchanger 6 and lines 7 and 8 into a first reaction zone 9after being combined in line 8 with a hydrogen-rich gas stream from line31 and a gas oil distillate having a boiling point within the range offrom 450 to 700 F., designated herein as wash oil from line 51.

Hydrogen purity in the hydrogen-rich gas stream is not critical and canbe between 30 to but it is preferred that the hydrogen-rich gas streamcontain between 50 to 100% hydrogen. The rate of addition of thishydrogenrich gas stream can be between 1500 and 10,000 s.c.f./ bbl. orhigher with preferred addition being in the range of 3,000 to 7,000s.c.f./bbl. Admixture of wash oil with the material charged to the firstreaction zone helps to insure against the formation of polymerizationproducts or deposition on the catalyst and also to control thetemperature rise across the catalyst in the reaction zone. Suchadmixture of wash oil with the unsaturated aromatics extraction feedfraction should take place as close to the point of contact between theadmixture and the catalyst as feasible to obtain proper mixing whileproviding as little time as possible for promoting thermalpolymerization. The temperature of the total charge to the first reactonzone is about 450 F. Operating conditions for the reaction zone itselfinclude a temperature within the range of about 450 to about 550 F. anda pressure within the range of about 200 to about 1200 p.s.i.g.

The partially hydrogenated effluent from the first reaction zone 9, at atemperature of about 500 to 550 F., passes through line 10 and afteradmixture with additional wash oil from line 52 passes through line 11into the second reaction zone 12 which it enters at a temperature ofabout 600 F. An elevated temperature of between 600 to about 700 F. ismaintained in the second reaction zone 12 to complete the saturation ofthe monoolefinic hydrocarbons and to convert nitrogenous and sulfurouscompounds into ammonia, hydrogen sulfide and hydrocarbons.

The total liquid product from the second reaction zone,

at a temperature of about 650 to about 700 F., is passed through line 13and combined with hydrocarbon fractions from lines 3 and 5. The combinedfractions in line 14 are then cooled with additional wash oil from line47 and introduced via line 15 at a temperature of about 450 F. into athird reaction zone 16. Mild conditions in this third reaction zone,including temperatures between about 450 to about 550 R, are maintainedto effect only partial hydrogenation of the unsaturated materialspresent in the feed introduced into this final reactor. As previouslyindicated, the totally hydrogenated effluent from the second reactionzone, together with the added wash oil, serves to dampen any temperaturerise efiiects in this third reaction zone.

The eflluent from the third reaction zone is passed via lines 17 and 19through one or more heat exchangers l8 and 20 prior to being passedthrough line 21 into high pressure separator 22. Separator 22 operatesunder essentially the identical pressure as reaction zone 16 and ineffect controls the operating pressure of 200 to 1200 p.s.i.g. andpreferably 400 to 800 p.s.i.g. maintained within each of the reactionZones. In fact, the operating pressure within separator 22 may beemployed as an indication of the quantity of make-up hydrogen which musthe added to the process via line 28. Separator 22 operates atessentially ambient temperatures of the order of 100 F. or less andserves to separate the total product effluent from reaction zone 16 intoa gaseous phase and a normally liquid hydrocarbon phase.

The gaseous phase, substantially rich in hydrogen but also containingammonia and hydrogen sulfide as well as light paratfinic hydrocarbons,such as methane, ethane and propane introduced with the make-up gas, iswithdrawn from the separator via line 23 and is passed to compressor 26via line 25. Compressed gas is then discharged into line 27 and aftersubsequent purification and/0r admixture with make-up hydrogen suppliedfrom line 28 is passed through line 29, heater 3t) and line 31 where itis then admixed with the fraction in line 7. At least a portion of thegaseous phase in line 23 is withdrawn or vented from the system via line24 for the purpose of preventing any undue buildup ammonia and hydrogensulfide in the system.

The normally liquid product efiluent from separator 22 is removed vialine 32 and is passed to a standard final separation zone comprising astabilizer 33 and a fractionator 36. Light gases are removed from thestabilizer via 34 while the remaining liquid hydrocarbons are passed vialine 35 to fractionator 36. At least three fractions are recovered fromthe fractionator, viz., a light gasoline fraction, via line 37; anaromatics fraction (normally, benzene, toluene and xylene), via line 38,which may be passed to a further separation or recovery operation (notshown); and a heavy gasoline fraction, via line 39. Bottom material inthe fractionator is recycled as wash oil and facilitates in the controlof the various temperature and flow rates within the process.

Thus, the wash oil is removed from fractionator 36 via line 40, passedthrough pump 41 and transmitted into line 42. Preferably, this wash oilis sent via lines 43 and 44 through heat exchanger 18 where it isemployed to cool the diluent from the third reaction zone. Optionallyhowever, the entire wash oil or a fraction thereof may be passed throughline 45 into line 46 for a recycle back into the system. As previouslydescribed, the wash oil in line 46 may be passed through line 47 toeffect temperature control in the third reaction zone and also throughlines 48 and 50 to 52 for control of the reaction in the first andsecond reaction zones. Tempreature of the wash oil supplied to the firstand second reaction zones is controlled by heater 49.

Periodically, it is desirable to purge a small amount of wash oil fromthe system. This may be accomplished via line 53. Make-up Wash oil, suchas No. 2 furnace oil or any other suitable gas oil distillate boilingwithin the range of 450 to 700 F., may be added to the system via line54.

Various modifications may be made to the illustrated embodiment by thosepossessing the requisite skill within the art of petroleum processingwhich do not remove the resulting process from the broad scope andspirit of the present invention as set forth in the appended claims. Forexample, separator 22 may be combined with additional separating and/0radsorbing means such as Water injection means for adsorbing ammonia fromlines 23 and/ or 24. Similarly, the gaseous phase from separator 22 maybe so treated as to effect substantially complete removal of hydrogensulfide and/or light parathnic hydrocarbons. Also, through the use of asuitable wash oil recycle storage vessel, the rate of wash oil recycledto each of the reaction zones may be controlled. In addition,hydrogen-rich gas may be separately introduced into lines 11 and/or 15in addition to the hydrog n-rich gas supplied to the system in line 31.Water or any other cooling media may be employed to effect heat exchangeof any feed or product line. Likewise, steam or any other suitableheating media may be utilized in the heat exchange system for increasingthe temperature of feed or product streams.

In some instances, it may be desirable to provide for multi-pointintroduction of the reaction charge at various sections of the reactionzones in order to maintain a desired heat balance in said zones. Fortemperature control in the reaction zones, it may also be desirable toprovide for alternate injection points for the wash oil. While theprocess of the present invention is most advantageously effected inthree reaction zones, additional reactors could be employed or one ormore of the reaction zones can be located within the same housing.

Reaction space velocity in the reaction zones is within the range ofabout 0.5 to about 10.0 or more LHSV with preferred space velocitiesbetween 1 and 4 LHSV (liquid hourly space velocity). Space velocity iscorrelated with reaction temperature and pressure to obtain the desireddegree of saturation in each reaction zone. In general, as the reactiontemperature increases, the space velocity also increases.

The quantity of wash oil which is recycled and combined with the chargeto the reaction zones is preferably such that the combined feed ratio toeach of said zones lies within the range of from about 0.5 :1 to about6:1 and preferably from about 0.5 :1 to about 2: 1.

The catalyst employed in each of the reaction zones may have the same ordifferent chemical and physical characteristics. Preferred catalysts aredisclosed in U.S. Letters Patent No. 2,880,171 and 2,993,868. Generally,suitable catalytic composities for utilization in th present processwill comprise metallic components selected from the group consisting ofGroups VI-A and VIII of the Periodic Table and compounds thereof. Aparticularly suitable hydrogenation catalyst is nickel supported on asuitable base such as silica, alumina, calcium carbonate, or any otherbase or mixture of one or more bases which has a low activity forcracking and polymerization reactions. Other desired metallic componentsinclude chromium, molybdenum, tungsten, iron, cobalt, ruthenium,platinum, palladium and mixtures of two or more of these components withor without nickel.

When the foregoing conditions of operation and processing techniques arefollowed, the process of the present invention is capable of effectingeflicient simultaneous partial and total hydrogenation of a full range,unsaturated hydrocarbon distillate, over extended periods of time. Thetendency of high molecular weight polymer and co-polymer formation aswell as a tendency for the formation of inhibitive amounts of coke andother carbonaceous materials is overcome so completely that the catalystin the reaction zone is active .for substantial periods. However, aswith virtually all catalytic conducted processes, there is a slow butnaturally-occurring deactivation of the catalyst Example I In accordancewith this example, the simultaneous treatment of pyrolysis gasoline (Cto 400 F.) is provided wherein the BTX (benzene, toluene, xylene)fraction of the raw feed is hydrogenated to the following specification:

Bromine number 1 Diene content Nil Sulfur 1 ppm. Nitrogen 1p.p.m.

and fractions other than BTX are partially hydrogenated to provide cuts,essentially free of gum-forming tendencies, suitable for blending intomot-or gasoline.

about 12:1 and introduced at about 450 F. into a third reaction zone.Pressure in each reaction zone is maintained at about 800 p.s.i.g. andthe space rate for each reactor is 2 LHSV based on the combined feed andwash oil. The efiluent product from the third reaction zone is thencooled to a temperature of about 100 F. and passed to a high pressureseparator.

A portion of the gaseous hydrogen-rich stream obtained from theseparator is vented, while the remaining portion is recycled andcombined with make-up hydrogen for addition to the liquid charge to thefirst reaction zone. The normally liquid product effluent, followingseparation in the high pressure separator, is passed to a conventionalstabilizer and then fractionated to obtain at least a light gasolineproduct (C product), an aromatics product (BTX fraction) and a heavygasoline product (C product). Remaining material is recycle as wash oilfor admixrture with the charge to each of the three reaction zones.

The overall material balance (excluding recycle wash oil) for thisoperation is shown in the following table. Amounts are given in poundsper hour.

Fresh Make-up Feed as Aromatics to 09 Extraction Product Cs Product VentGases The catalyst composite within each of the thre reaction zones iscomposed of 0.2% nickel, 1.7% cobalt and 9.5% molybdenum deposited on analumina support. This catalyst composite is prepared by first calciningthe alumina base at an elevated temperature of about 1100 F. Molybdenumis then deposited on the calcined base from a solution prepared bydissolving ammonia paramolybdate in ammonical water solution. Afterdrying, the material is calcined at 900 F. for about 10 hours. Thecobalt and nickel metals are deposited upon the molybdenum-aluminamaterial from a water solution of the metal nitrates. After drying, thematerial is again calcined at a temperature of about 900 F. for about 10hours.

The raw charge stock is initially fractionated to provide a lightunsaturated gasoline fraction having an end boiling point of about 160R, an unsaturated aromatics fraction having a boiling point range ofbetween about 160 to about 295 F. and a heavy unsaturated gasolinefraction having an initial boiling point of about 295 F. Forconvenience, these fractions will be referred to hereinafter as the Cfraction, the BTX fraction and the C fraction, respectively.

The BTX fraction is blended with previously recycled Wash oil in acombined feed ratio of about 2:1 and about 1500 s.c.f./b.b.l. ofhydrogen-rich gas. This mixture enters the first reaction zone at aninlet temperature of about 450 F. Reactor effluent from the firstreaction zone having a temperature within the range of 500 to 550 F. isthen admixed with additional wash oil in a combined feed ratio of about1.211. This admixture is then introduced into the second reaction zoneat an inlet temperature of 600 F. The C and C fractions are blended withthe second reaction zone effiuent, combined with additional wash oilrecycle in an amount to result in a combined feed ratio of It can beseen that the BTX fraction is processed for complete hydrogenation ofolefins and diolefins while the C and C fractions are simultaneouslyprocessed in accordance with the present invention for hydrogenation ofcycloand di-olefins. Mono-olefins are retained in these latter fractionssince they do not significantly contribute to the formation of gums ingasoline and they have a desirable octane rating.

Example II The feedstock employed in this example had the followingcomposition.

This feedstock is processed substantially according to Example I withthe exception that in the final product fractionation step only twoproducts (C product and an aromatic stream) are recovered. It is to beunderstood, however, that the product aromatic stream may be subjectedto additional and subsequent treatment to effect the separation of theBTX materials and the C materials.

The overall material balance, (excluding recycle Wash oil) for thisoperation is shown in the following table.

Amounts are given in the table as pounds per hour.

Raw Make-Up HgPun'. Vent Stab. C5 Feed Gas Reject Gases Off-GasAromatics to Product Separation TotaL- 48,863 1, 000

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore, only such limitations should be imposed asare indicated in the appended. claims.

What is claimed is:

1. .A process for the simultaneous partial and total hydrogenation ofselected distinct fractions of unsaturated hydrocarbon distillate whichcomprises initially fractionating said distillate to provide a lightfraction having an end boiling point of about 160 R, an unsaturatedfraction having a boiling point range of about 160 to 295 F. and a heavyfraction having an initial boiling point above about 295 F.; reactingsaid unsaturated fraction with hydrogen in a first reaction zone at atemperature of about 450 to about 550 F.; reacting the effiuent from thefirst reaction zone in a second reaction zone at a temperature of about600 to about 700 F.; combining the reaction effiuent from the secondreaction zone With the light fraction and the heavy fraction; reactingthe resulting combined mixture in a third reaction zone at a temperatureof about 450 F. to about 550 F. and separating the efiiuent from saidthird reaction zone into 2. The process of claim 1 wherein the wash oilis admixed With material charged to at least one of the reaction zonesin an amount to result in a combined feed ratio to the reaction zone ofabout 0.521 to about 6: 1.

3. The process of claim 1 wherein the catalyst composite comprisesmolybdenum and at least one metallic component from the metals of theiron group of the Periodic Table.

4. The process of claim 1 wherein the reaction space velocity in thereaction zones is between about 1 and 4 LHSV.

5. The process of claim 1 further characterized in that the pressure inthe reaction zones is between about 200 and 1200 p.s.i.g.

References Cited UNITED STATES PATENTS 3,133,013 5/1964 Watkins 208-1433,161,586 12/1964 Watkins 208-443 3,239,449 3/1966 Graven et al. 208-143HERBERT LEVINE, Primary Examiner.

